Glass-fibre-reinforced plastic container

ABSTRACT

Glass-fibre reinforced plastic tank, for example for liquid petroleum gas under high pressure, compressed air for air brakes or for storage of acetylene. The tank is composed of two halves, the open ends of which are conically bevelled to form a male end and a female end, which are joined to each other by an adhesive. The reinforcement in the outer and inner layers of the halves contains essentially longitudinal glass-fibre strands and the intermediate layer contains essentially longitudinal glass-fibre strands and the intermediate layer contains essentially transverse glass-fibre strands. In the half with the male end, the longitudinal glass-fibre strands in the inner layer are densely located adjacent to each other, while the longitudinal glass-fibre strands in the outer layer lie in separate groups of densely arranged glass-fibre strands with the predetermined spacing between the groups to form channel-shaped spaces. In the half with the female end, the order is reverse. In order to store acetylene, a pre-fabricated absorbent body of porous material is enclosed in the tank when the tank halves are glued together.

This application is a divisional application of Ser. No. 08/352,282filed Dec. 8, 1994, now pending, which in turn is a divisionalapplication of Ser. No. 08/142,476 filed Nov. 22, 1993, now abandoned.

The present invention relates to a glass fibre reinforced plastic tankfor liquified petroleum gas, compressed air or acetylene gas, a methodof manufacturing such tanks and an apparatus for manufacturing suchtanks. Other reinforcing strands than glass fibre strands can also beused.

Swedish patent application 9001841-7 describes a glass fibre reinforcedtank of the type in question which has in the conical joint between thetwo container halves, a special arrangement of the joint surfaces toenable the tank to withstand relatively high pressures, up to about 100bar, for example.

The two tank halves in the known tank have outer, inner and intermediatelayers, comprising densely laid fibre glass strands, which prior tocasting of the tank form a separate reinforcing body which is laid inthe mould. These glass fibre strands have, prior to manufacture of thereinforcing body, been included in strip shaped collections of glassfibres or roving.

During casting, however, the densely laid reinforcing strands providerelative large flow resistance to the plastic and thus require arelatively high pressure for injection into the mould. It is of coursedesirable to be able to fill the mould with as many glass fibre strandsas possible in order to obtain the corresponding high strength in thetank, but up to now it has not been possible to achieve a greater degreeof filling than about 30% by weight glass fibre strands. The injectionpressure is limited by the fact that if the pressure is too high, thereinforcing body will be axially compressed.

One purpose of the present invention is therefore to provide a glassfibre reinforced tank with a substantially increased amount of glassfibre strands than 30% by weight in the reinforcing body.

This is achieved with a tank which, according to the invention, has thecharacterizing features disclosed. The tank is manufactured with channelforming spaces between the groups of glass fibre strands in the outerlayer of the male part and in the inner layer of the female part. Thesechannels form during casting flow channels for the plastic material, sothat it can be spread readily out from the channels and thus facilitatedispersion of the plastic material to the various portions of thereinforcing body. No appreciable increase in pressure is necessary toinject the plastic into the mould, while increasing the amount of glassfibre without any problems to about 60% by weight, which provides acorresponding increase in the strength of the tank. With the small coneangle in question for the conical bevel portions of the ends of the tankhalves, i.e. 2-10°, there will be a correspondingly long overlap of thedensely and thickly laid glass fibres in the outer layer of the femalepart and in the inner layer of the male part, while retaining thestrength of the joint. As a whole, the tank will be somewhat weakened bythe channel spaces in the outer layer of the male. Portion and in theinner layer of the female portion, but this weakening is marginalrelative to the appreciably increased strength due to the possibility ofincreased filling with glass fibres.

However, the invention also is intended to make it possible to use thetank for acetylene gas. Previously known tanks have consisted of twometal halves welded together. A porous paste has been pressed throughthe connection opening of the tank and thereafter been sintered byheating the tank. This method cannot course be used for a plastic tank,since the filler paste pressed into the tank cannot be sintered byheating. Conventionally, a known acetylene tank or ackumulator is filledwith a porous filler, also called "AGA paste", which according to aknown recipe consists of charcoal, diatomaceous earth, asbestos andcement. The paste is introduced into the tank in a wet state, and thetank is then dried in a kiln. When the water vapour thus leaves thepaste, it becomes particularly porous, the pores assuming about 80% ofthe entire volume of the tank. The tank is filled with acetone which isabsorbed by the porous material. Acetone is a liquid which is capable ofdissolving large amounts of acetylene and this dissolving capabilityincreases with increased pressure, and thus it is possible in a solutiongas tank to store acetylene in liquid state at reasonable pressure. Whenthe gas is taken out of a filled solution gas tank, the liquid leveldrops and there will be a free gas volume in the upper portion of thevertically standing tank. If there should be cause for an explosion inthis gas quantity, it will however be prevented by the porous material,since an explosion cannot be propagated in the very small channelscontained in this material. The material fills essentially the entirevolume of the tank but shrinks somewhat during drying or sintering, andtherefore it cannot completely fill the tank, and this is a disadvantagein view of the risk of explosion. Since the water vapour during dryingcan only escape through the tank opening, this drying operation takesquite a long time. A drying period of a week or more is not uncommon.The manufacture of acetylene tanks according to known technology is thusquite complicated, time-consuming and thus costly.

An additional purpose of the invention is therefore to provide a plastictank, containing a sintered porous filler body, which can then absorbacetone and acetylene gas.

This is achieved by a tank as disclosed herein. The solution of theproblem in question is thus extremely simple according to the invention,since it presents no particular difficulty to prefabricate a sinteredfiller body which fits exactly into the halves of the plastic tank asthey are assembled.

By suitably adapting the moulds for the plastic halves, a filler bodywith exactly calculated outer dimensions can be prefabricated. The bodycan then be inserted with perfect fit into the two tank halves, whichare then glued together to form a finished tank. The mould for thefiller body can be made separably or provided with evacuation channels,so that the filler body for drying in a heat chamber can be removed inits entirety from the mould.

Alternatively, water vapour from the filler body paste can be divertedthrough specially designed evacuation chambers. Thus the remainingmoisture can be purged in the form of steam at a fraction of the timerequired by the conventional method. The total outer surface of thefiller body can be exposed, for example, to a stream of hot air or befurther treated in the heat chamber after the filler body has beenremoved from the form.

One precondition for being able to manufacture the filler bodyseparately and being able to insert it in its finished state into theplastic tank is that the tank be made in two halves according to theinvention, which fit exactly over the filler body and thus can bejoined, in closing the filler body, and then be glued together. If thetank should be made in a conventional manner in metal, it would benecessary to weld the two halves together. Welding involves, however,very high temperatures at the weld, thus damaging the portion of thefiller body located adjacent the weld, thus creating cavities whichcould increase the risk of explosion. By enclosing the filler orabsorption body in a plastic tank consisting of two fibre reinforcedhalves, the joining of the halves can be carried out at room temperatureor slightly thereabove (about 50° C.) by gluing without affecting thedegree of filling of the filler body in the tank.

Since the filler body shrinks somewhat during drying and sintering, itis advisable to start with the shape of the finished filler body andmake the mould for the halves of the plastic tank from the shape of thefiller body, thus assuring exact fit of the filler body in the inside ofthe plastic tank.

An additional purpose of the invention is to provide a method formanufacturing the reinforcing bodies included in the tank halves and asimple apparatus for carrying out the method. This is achieved by amethod and an apparatus according to the invention which have thecharacterizing features disclosed herein.

Suitable embodiments of the tank according to the invention are shown asexamples in the accompanying schematic drawings, and will be elucidatedbelow in the following description. Also described below is a methodaccording to the invention of manufacturing the tank and one embodimentof an apparatus for manufacturing the reinforcing glass fibre bodiesincluded in the tank.

FIG. 1 is a side view of the container consisting of two cylindricalhalves. Each half is made in one piece and has a bottom.

FIG. 2 shows in a larger scale a section along the line 2--2 in FIG. 1,leaving out the fibre-glass reinforcement.

FIG. 3 is a schematic representation in longitudinal section of the endportion included in the joint of the female part in FIG. 2.

FIG. 4 is a schematic representation of the strand orientation incross-section along the line 4--4 in FIG. 3, showing the reinforcingbody laid between the inner and outer portions of the mould.

FIG. 5 is a schematic representation of the strand orientation inlongitudinal section of the end portion of the male part.

FIG. 6 is a schematic representation of the strand orientation incross-section along the line 6--6 in FIG. 5 and shows the reinforcingbody laid between the outer and inner portions of the mould for castingthe tank half shown in FIG. 5.

FIG. 7 shows a finished filler or absorbent body of porous materialdesigned to fit into the finished plastic tank. The absorbent body iscompletely inserted into one tank half and only partially into the othertank half.

FIG. 8 shows an alternative embodiment of the tank halves and the fillerbody.

FIG. 9 shows schematically in section a moulding tool for producing thereinforcing bodies of glass-fibre strands for the tank.

The tank in FIG. 1 is composed of two cylindrical halves 10, 12, each ofwhich has a bottom 14, 16, respectively. In the joint between the twohalves, the end portion 20, which is a male portion, is inserted intothe end portion 22 so that the internal glueing surface 26 of the endportion 22 will lie precisely against the external glueing surface ofthe end portion 20 to thereby achieve effective adhesion therebetween toform a glueing joint which provides an air-tight seal against the gasunder pressure in the tank, said pressure being in the range of 2-60bars. The glue joint 25 can also absorb substantial tensile and shearingstresses.

In order to increase the resistance of the joint to external stresses,e.g. in the form of blows, bumbs or heating, the joint is provided witha protective sleeve 40, which consists of glass-fibres which have beenwound in the form of a glass-fibre roving about the joint and providetogether with a suitable UV-curing plastic an insulating protectingsleeve. According to a preferred embodiment, the protective sleevecomprises an inner layer 42 of polyurethane foam, with a suitablethickness of 2 mm and a thin outer cover layer 44 of glass-fibrereinforced plastic and with a thickness of about 1 mm.

FIGS. 3 and 4 show the orientation and placement of the reinforcingstrands in the end portion 22 of the female part according to theinvention. FIG. 3 shows the end portion in longitudinal section whileFIG. 4 shows the same part in cross-section. The conical joint surface26 cuts through three different reinforcing layers of plastic andreinforcing strands. According to the invention, an outer layer 32 andan inner layer 36 are each composed of longitudinal reinforcing strands,while the intermediate layer 34 is composed of a number of courses oftransverse reinforcing strands. The outer layer 32 extends out to thethinnest portion of the end portion 22. The inner layer 36 terminates,however, in the joint surface at the thick portion of the end portion22. The longitudinal reinforcing strands in the outer layer are denselypacked in a number of courses, while the longitudinal strands in theinner layer 36 are laid in flat groups of densely arranged reinforcingstrands with a predetermined space between the groups. This provideschannel spaces 38 between the groups 37 of densely arranged reinforcingstrands or roving.

The groups 37 form flat collections of glass-fibres. The width of thechannels F between the groups is suitably at least half of the width Eof each group.

FIGS. 5 and 6 show the orientation and placement of the reinforcingstrands in the end portion 20 of the male part according to theinvention. FIG. 5 shows the end portion in longitudinal section, whileFIG. 6 shows the same portion in cross-section. The conical jointsurface cuts through three different layers of glass-fibre strands,which are enclosed in plastic material. An outer layer 29 and an innerlayer 35 are each composed of longitudinal reinforcing strands, while anintermediate layer 33 is composed of a number of courses of transversereinforcing strands. The outer layer 29 ends at the joint surface in athicker portion of the end portion 20. The inner layer 35 extends,however, out to the thinnest section of the end portion 20. Thelongitudinal reinforcing strands in the inner layer 35 lie denselypacked in a number of courses while the longitudinal threads in theouter layer 29 form groups 30 of densely arranged reinforcing strandswith a predetermined spacing between the groups. This provides channeledspaces 31 between the spaced groups 30 of densely packed reinforcingstrands. In this case as well the spacing between the groups is at leastequal to half of the width of each group.

FIGS. 4 and 6 indicate how the inner and outer mould walls A and B,respectively, were disposed in the mould, into which the glass-fibrestrand reinforcing body C and D, respectively, were placed beforeplastic was injected into the mould. Plastic injected into the bottomend of the mould flows through the channels 31 and 38, respectively, atrelatively high pressure to initially fill out the spaces between thestrands in the inner layer 36 in FIG. 4 and the outer layer 29 in FIG.6. From there the plastic flows from the channels essentially radiallyin between the transverse glass-fibre strands in the intermediate layers34, 33 and continues radially between the longitudinal fibre strands inthe layers 32, 35.

Thanks to the channels 38, 31 the plastic will, due to its radial flowfrom the channels, have a shorter path for spreading out into thereinforcing body, which in turn means that there will be less resistancecomparison to previously known reinforcing bodies, which have a fibrepercentage of about 30% by weight. The pressure could thus be reducedwhile still retaining the same dispersion of plastic. If one wishes,however, to retain the pressure at a relatively high level, this can beutilized to overcome the resistance of the greater percentage of fibresin the reinforcing body according to the invention. Tests performed haveshown that it is possible without difficulty to increase the percentageof fibres to about 60% by weight.

FIG. 7 shows the filler body 45 with tank half 10 completely in placeand tank half 12 partially slipped into place. The external dimensionsof the body 45 agree precisely with the inner dimensions of therespective tank halves, and this means that each tank half can beslipped tightly under the cylindrical lateral surface of the body 45 asshown by the arrow, until the conical joint surfaces of the end portions20 and 22 make contact for glueing. The tank is provided with an opening15 for filling and dispensing a fluid. The filler body 45 thuscompletely fills out the entire volume of the tank except for the areaaround the opening where a small gap or slit a has been left about theopening to increase the evaporation surface for acetylene when the tankis in its vertical position for use, as shown in FIG. 8. The gap isabout 2 mm about the opening and decreases radially outwards. The gapcan be partially filled with radial ribs on the inside of the tank or onthe end of the filler body in order to take up any axial forces when thetank is subjected to impact, i.e. when the vertical tank is dropped froma certain height.

FIG. 8 shows a tank according to the invention equipped with a fillerbody or absorbent body 45 made of a porous material which is known perse and which is intended to contain acetylene dissolved in acetone in aknown manner.

In the preferred embodiment of the filler body according to FIG. 8, thefiller body 45 has the shape of two truncated cones pointed away fromeach other with a common base surface and a cone angle in the range of1-7°. Each tank half 10 and 12, respectively, has an internal shapeagreeing with the respective cone so that the filler body 45 in thiscase as well fills out the entire volume of the tank without any gaps orspaces being formed in the boundary between the wall of the tank and thefiller body, except in the area about the opening 15. The conical shapemakes it easier to achieve exact fit when assembling the tank and theenclosed filler body. A certain amount of elasticity prevents the fillerbody from shrinking after a period of use and giving rise to undesirablegaps.

The male part 10 and the female part 12 are manufactured by a methodaccording to the invention. According to this method, first severallayers of longitudinal and transverse glass-fibre strands are built upon a core with the aid of a robot, thus forming a reinforcing body ofglass-fibre strands. The glass-fibre strands building the reinforcingbody are fixed in a known manner relative to each other by spraying on aresin powder slurried with water, whereafter heating takes place in aknown manner to bind the glass-fibre strands to each other to achieve afinished reinforcing body. This body is placed in a mould which issealed and molten plastic is then pressed through the mould gate. Themould is then heated to 50° C., whereupon the plastic sets and the tankhalf is removed from the mould.

The reinforcing body for the male part 10 has a male end 20 and ismanufactured by winding on a core 50, the preforming tool, at least onelayer of longitudinal reinforcing strands densely arranged. A robotfirst fixes a roving of reinforcing strands on hooking means 56 locatednear the lower portion of the form. Said roving is drawn up along a path52 on the form until it is in level with the upper closed end thereof,whereupon the fibre roving is drawn diametrically across said end andthen downwards along a diametrically opposed path on the form to behooked on second hooking means 57, which are opposed to the firsthooking means and are also located near the lower portion of the form.

One then continues to lay the fibre rovings closely adjacent to thepreceding course and hook the fibre rovings on additional hooking means(not shown), repeating the sequence a predetermined number of timesuntil a predetermined density between the rovings is achieved and thelager of a predetermined number of roving courses is achieved. A layerof transverse densely arranged bundles of fibres is then wound on thelayer of longitudinal fibres, said layer being wound with a number ofcourses on each other depending on the required stress tolerance of thefinished tank. On top of this layer of transverse fibres, there isfinally wound with the same procedure as in the previously wound innerlayer an outer layer of longitudinal fibre rovings, which are collectedin groups of densely arranged fibre rovings with a predetermined spacebetween the groups so that channel-shaped spaces are formed betweenthem. The female part 12 with the end 22 is made in a correspondingmanner but in the reversed order, i.e. the layer with channel forminglongitudinal groups of fibre rovings is wound first, and thereafter thetransverse layer and finally the layer with longitudinal reinforcingstrands, wound closely to each other in a number of courses.

By making the reinforcing body of the male part and the female part asdescribed above, there is obtained after casting and curing a male part,the reinforcement of which for absorbing axial forces is locatedessentially in the layer closest to the interior, and a female part, thereinforcement of which for absorbing axial forces is located essentiallyin the layer closest to the exterior. The cast male and female parts arethen finished by cutting off the protruding glass-fibre reinforcingstrands from the open ends, whereafter the end portion 20 of the malepart is conically bevelled with a cone angle α and the end portion 22 ofthe female part is bevelled to a corresponding inner cone angle α. Thetwo halves can now be joined together to form a tank by applyingadhesive to the joint surfaces 24, 26, which due to the simple bevellingcan be easily moved into contact with each other.

The joint is then provided with the heat insulating and impactprotecting sleeve 40 comprising polyurethane foam, which, for example inthe form of a 2 mm thick strip 42 has been wound around the joint. Thestrip 42 is then covered by a covering layer 44 of fibre reinforcedplastic which can consist of reinforcing strands, such as glass-fibrestrands, wound about the joint together with a suitable UV-curingplastic to provide the stiff covering layer 44.

The apparatus for manufacturing the reinforcing bodies included in thetank comprises a winding robot (not shown) with feeder nozzles forfeeding glass-fibre rovings, a preshaping form 50, a spray head forspraying meltable resin powder slurried in water and a heat chamber (notshown) for heat treating a finished reinforcing body. The preshapingform 50 has a vertical cylinder 52 on the upper angular end of which abowl-shaped cap 54 rests. The cap is connected to a pneumatic cylinder60, thus making it possible to raise and lower the cap 54 in thedirection of the double arrow to facilitate removal of a finishedreinforcing body. At the bottom of the form there is an additionalpneumatic cylinder 58 for retracting or extending through openings inthe wall of the form, hingedly fixed hooking means 56, 57, e.g. steelwires such as bicycle spokes. The fixing points of the hooking means canthus be raised or lowered in the directions of the smaller double arrow.Each cylinder is operated via pressure lines connected to correspondingpneumatic connections 62.

When a reinforcing body is to be wound, the piston rods of the twopneumatic cylinders 58, 60 are retracted. Thus the cap 54 will rest onthe upper angular end of the cylinder 52 and form together with thecylinder a core for winding a reinforcing body for a male part or afemale part. The ends of the hooking means 56, 57 hinged to the pistonrod of the cylinder 58 are thus in their lowermost position, in thisposition, the ends of the means extend a predetermined distance outsidethe lower cylindrical wall portion of the form 50. The fibre rovings tobe wound into a reinforcing body are hooked onto the hooking means andare drawn up and over the core as described previously. After thereinforcing body has been wound and fixed by spraying resin powderslurried in water followed by heat setting, the finished reinforcingbody is to be removed from the form. Compressed air is therefore sent tothe pressure side of the cylinder 58 to press the piston rod out and theends of the hooking means 56, 57 hinged to the piston rod will assumetheir uttermost position and the protruding ends of the means will bepulled in through the openings in the cylindrical wall of the form 50.By directing compressed air to the connection 62 which is joined to thecylinder 60, the piston rod is pressed out lifting the cap 54 from theupper edge of the cylinder. The finished reinforcing body is thus liftedup by the cap 54 so that it is displaced a corresponding distance andcan be lifted off the form 50 with the aid of a conventional grippingmeans and be placed in storage or be further treated directly bytrimming the end and grinding the respective conical joint surface forsubsequent placement in the casting mould for casting a tank half.

I claim:
 1. Plastic tank reinforced with glass-fibres or correspondingreinforcing filaments, and composed of two generally cylindrical tankhalves, each having a bottom, one of said bottoms having a connectingopening, the open ends of said tank halves being conically bevelled andinserted into each other as a male part in a female part and heldtogether by an adhesive, said tank halves having outer and inner layerscontaining essentially longitudinal reinforcing strands and anintermediate layer containing essentially transverse reinforcingstrands, the inner layer of the male part containing a layer of denselyarranged reinforcing strands in a number of courses of flat-lyingrovings, the outer layer of said female part containing a layer ofdensely arranged reinforcing strands in a number of courses offlat-lying rovings, and said cone angle in the conical joint being inthe interval 2-10° characterized in that the outer layer (29) of themale part (20) and the inner layer (36) of the female part (22) comprisereinforcing strands in flat-lying rovings forming groups (30, 37) with apredetermined lateral spacing (F) between the groups to form channels(31, 38), in which plastic has been introduced during casting of therespective tank half (10, 12) to facilitate dispersion of the plasticbetween the reinforcing strands in the respective tank half.
 2. Plastictank according to claim 1, characterized in that the groups (30, 37)have essentially the same lateral width (E), and that the spacing (F)between the groups is at least equal to half of said width.
 3. Plastictank according to claim 1, characterized in that the tank comprises aporous filler or absorbent body (45) for acetylene dissolved in acetonefor tapping acetylene through the connecting opening (15) at one end ofthe tank, that the absorbent body (45) is prefabricated with the sameshape as the inner shape of the tank, that the respective tank half (10,12) is slipped onto the finished absorbent body (45) and that thecontainer halves (10, 12) are moved together and joined to each other atthe male and female parts (20, 22).
 4. Plastic tank according to claim3, characterized in that the tank halves (10, 12) are cast with the aidof a mould (50) which is produced with a finished absorbent body (45) asa core in order that the absorbent body (45) will exactly fill out thespace in the finished tank.
 5. Plastic tank according to claim 3,characterized in that the absorbent body (45) is slightly conical fromthe centre out towards the ends, and that the tank halves (10, 12) havea corresponding conical shape to provide a sealing contact between theabsorbent body (45) and the inside of the tank (10, 12).
 6. Plastic tankaccording to claim 3, characterized in that the absorbent body (45) andthe tank (10, 12) are made in such a manner that a residual space or gapis provided in and about the connecting opening (15) of the tank, inorder to increase the surface of the absorbent body (45) from which theacetylene gas leaves.